Apparatus for determining energy delivered to a pile



June 8, 1965 c, GUlLD ETAL 3,187,553

APPARATUS FOR DETERMINING ENERGY DELIVERED TO A PILE Filed Nov. 15, 1961 2 Sheets-Sheet 1 INVENTORS CHARLES GUILD PERLEY B. KIMBALL M I fiml www- ATTORNEYS C- L. GUILD ETAL June 8, 1965 APPARATUS FOR DETERMINING ENERGY DELIVERED TO A PILE Filed Nov. 15, 1961 2 Sheets-Sheet 2 m n O A Ul. VGK m B mm R Am WE a 2 3 1111111111111 l I l 1 I I I i I'll I. flw mrll. ml] -l Ffl I||l|L 1| mozoomm l l l l l l l l I l l l l l ll 5 O 0 O O 3 2 l 0 O MW 3 N I P 5m W e H A 6 5 m m w l N P G G F D W P W H l I. II T R 5 R A |4T M 4 mm m ATTORNEYS capabilities of the pile.

3,187,553 V t APPARATUS FOR'DETERMJNING ENERGY DELIVERED TO A PILE V Charles L. Guild, 22 Woburn St., and Perley B. Kimball,

355 Pleasant St., both of East Providence, RI.

Filed Nov. 15,1961, Ser. No. 152,598

. 3 Claims. (Cl. 73-11) This invention relates to an apparatusfor recording the amount of energy delivered to an earth driven pile, and more particularly to a pile which is driven by sustained elastic vibrations as disclosed in the Bodine Patent No. 2,975,846.

Briefly, apparatus of this general nature as described in the referenced patent energizes a pile to a near-resonant frequency by the use of a mechanical oscillator. The energy developed in the pile by this energization is transmitted to the earth displacing it. From a physical standpoint the pile rapidly penetrates the earth or other strata through which it is being driven at a rate which is something on the order of twenty times as fast as a pile driven by the use of a conventional type impact hammer. Because of this rapid speed it becomes necessary to develop new methods of determining the load-bearing capabilities of a pile. In the past for an impact hammer driven pile engineers have used formulas to predict its load-carrying capability. These formulas generally state that the load bearing capacity for a pile driven by a single-acting steamhammer, based upon a factor of safety of six, is equal to two times the weight of the striking part of the hammer, in

pounds, times the fall of the striking part, in feet, divided by the sum of the set of the pile under the last blow, in'

inches, plus one tenth or [2wh/ (s+0.1)]. In driving a pile through the use of elastic vibrations it is apparent that there is no such thing as an identifiable blow (within the meaning used in the formula), and consequently there is no correlation for the set under the last blow in inches.

Basically, however, it will be noted that this formula" measures one quantity, namely, the gross energy delivered by the hammer to the pile. It does not take into account the net energy that is required to place the pile into position to support a specific load since there are many unknowns in the driving of piles by the conventional methods such as the energy lost in suchdriving caused by such things as heating, the hammer rebound, the pile'rebound and the elastic deformation and recovery of the pile as well as the shock waves in the surrounding soil and nearby structures. Accordingly, the formula is an empirical ap-' proximation which is based upon a wealth of engineering data with numerous load settlement tests. 'To make comparisons of piles driven by using oscillators resonating the pile, it is obvious that by proper instrumentationone can obtain the number of sonic impacts in the last foot or the last increment of time and further willlknow the horse- Accordingly, it is an object of the present invention to develop an apparatus for measuring the energy delivered to the pile in the last increment of drive thereof and use this energy and determination to predict the load-bearing Another object of the invention is to provide a means for measuring and recording continually the rate of fiow of energy to the pile andthe rate of penetration of the pile into the earth and record these quantities on a chart whose X-axis, or ordinate, is time. i

7 With these and other objects in view, the invention consists of certain novel features of construction ar d/or procedure which .will be more fullydescribed and particularly pointed out in the appended claims.

' nected to form a Wheatstone bridge 41 so that when i i [3,137,553 Patented June 8, 1965 instrumentation; 10

FIGURE 4 is adetail of the method of mounting a tachometer generator associated with this instrumentation;

FIGURE 5 is a schematic of the electrical circuit; and

FIGURE 6 is a graph of a typical set of curves. I

InFIGURE 1 there is shown a set-of leads generally designated 19 which areassociated with a pile driving apparatus and which are supported in a vertical direction or in any other angular direction necessary for driving a pile by a boom and other-apparatus familiar to those skilled in the art. The leads consist of a rectangular framework having one open side defined in the present embodiment by a pair of cylindrical members 11 and 12. Each of the cylindrical members has a web 13 and 14 extending radially outward from the cylindrical members 11 and 12, respectively, and the cylindrical members together with their webs serve as a vertical guide frame for a mechanism generally designated 15 that provides the motive power to effect the driving of the pile into the earth or other strata. The present mechanism for effecting this driving is shown as a mechanical oscillator 16 which is driven by an internal combustion engine 17 having a shaft coupling 18 which directly leads to the mechanical oscillator. The mechanical oscillator 16 and its engine 1'7 are guided onthe leads 11 and 12 by a frameworkhaving two vertical channel pieces 19 and 20, one degree of guidance being provided by at least two pairs of rollers such as 21, 22 which engage the edge of the webs 13' and 14, respectively, together with at least another pair of rollers not shown which engage the sides of the webs 13 and 14. The apparatus thus far described is capable of driving a pile into the ground by attachinga pile such as P to the lower end of the mechanical oscillator 16 as at 23 and driving the oscillator 16 by the engine 17 at a frequency such as is described in the Bodine Patent No. 2,975,846. Because strain gauges are mounted at an angle of to the axis of the shaft. These strain gauges are contwo opposite diagonals of the bridge are energized with an input voltage proportional to speed, indicated at 42, the other two diagonals will create an output voltage vacross leads 43' depending upon the balance or' unbalance thereof; Essentially, the strain gauges measure the torsion of the shaft ,as'it is loaded and by being suitably 293. This torque pickup is indicated by reference nu- V meral 25 and its output is connected basically to a re-- calibrated will measure the torque being transmitted by the shaft to its load. The shaft and apparatus are more fully described in Patents No. 2,350,972 and No. 2,392,-

cordinginstrument such as -'a strip chart recorder 44.

In addition to measuring the power being delivered by the engine, 'it is essential that we measure the rate rather a' special section of a shaft upon which bonded wire times total time in minutes.

of penetration of the pile into theearth. To accomplish this result, there is aifixed to the channel 19 a tachometer generator 26, the wheel of which is adapted to engage the side of the web 13. The tachometer generator 26 is shown in more detail in FIGURES 2, 3 and 4,.and by referring to these figures it will be seen that a space is provided above the guide wheelsZl in the channel 19. A bracket 27 is secured to the channel 19 by cap screws 28 and has a right angular portion as at 29extending into overlapping relationship with the opening in the channel 19. A shelf 30 extends at right angles from the portion 29 and pivotally receives thereon a mounting lug 31 of the tachometer generator 26. Attached to'the shaft of the tachometer generator is a wheel 32 which engages the side of the web 13 and a pull spring 33 at- ,tached between the tachometer and the shelf 30 urges this wheel 32 into engagement with the side of the web at all times. Accordingly, as the entire framework of the piledri-ving mechanism moves downwardly, the movement of the wheel 32 thereof will rotate the tachometer generator and produce a voltage output that is in proportion to the speed with which the wheel 32 is rotated. This voltagecan be fed to a galvanometer of a strip recorder which will move the pen of the strip recorder.

In addition to these two instruments, a standard electric tachometer 45 is coupled to the shaft of the engine, the output of which feeds the torque meter and also feeds a galvanometer moving a pen on the strip chart recorder 44 so that three .curves'appear on the strip chart, namely, the rate of. penetrati-om'the engine'speed and the engine power. We know, therefore, that the total energy delivered to the pile is proportional to the area under the engine power curve and the energy delivered in any inincrement under this same horsepower curve corresponding to the unit of time over which it is desired to measure the same. If it is desired to know the energy at any particular time, we can take the data directly-off the curves being drawn on the strip chart recorder since the energy curve in horsepower is shown. Further, if desired, directly off the strip chart we can obtain a correlation of the strata through which the pile is being driven. This is done by looking at the rate of penetration curve and noting the changes in slope. The horsepower curve is also an approach to noting the strata changes, for if one approaches a hard layer, the energy delivered to the oscillator will increase and the slope of the curve drawn will change enabling an operator to establish corrective control.

In summary, therefore, it will be seen that the data obtained from this recording system is in the form of three rate time curves. The HP. curve is equal to 550 times ft. lbs. per second on a time base; the rate of penetra-.

tion curve is feet/second on a time base; and the revolutions per minute on a time base. It follows, of course,

c'rement of time or 'of depth is proportional to the area that the area under each curveis proportional to a total quantity. Thus the total energy equals average H.P.

divided by 550 times total time in seconds. Similarly, the total penetration will be the averagefeet per second 7 times total time. in seconds, and the total revolutions of theengin'e will be the average revolutions per minute None of the curves, of course, have a constant slope which means that the rates are not constant. To analyze the matter, therefore, areas under the curves must be either obtained graphically or mathematically. For example,

t E pdt he to a where Ezenergy' pzpower t zinitial time p and '1 being related through the general expression p equals '(t). In order to come up with an expression that can be used by engineers in foundation engineering, we really want to find theenergy required to drive the last increment of depth, which may be one foot or one inch, rather than the total energy. Thus the short segment of the curve in which we are interested and which is represented by the definite integral must be ascertained. Obviously, the average value of p or power in any instant is readily found on the curve, and hence it may be said that the energy is equal to the average value of power times the time interval over which it is desired to take the sample and which would be the last inch or foot or other unit as mentioned. The formula, therefore, becomes:

where t ztime at start of final increment. The force required to drive the final increment of depth is:

X (tr-ix) sec.

E (in foot pounds) D (in feet) The above is analogous to the formula mentioned at the beginning of this specification. It thus forms a basis upon which correlation maybe had by load tests that are common to the engineering field.

We claim:

I. In a pile driver having a driving means supported in leads, an apparatus 'for determiningthe load bearing capacity of a pile comprising means for continuously recording on a common time unit scale the power delivered to the driving means, means for continuously reicording the rate of penetration on a common time unit scale, and means for continuously record on a common References Cited by the Examiner UNITED STATES PATENTS 2,392,293- 1/46 Ruge 73-136 2,580,299 12/51 Hunicke 7311 X 2,691,300 10/54 Morris 73-136 2,732,713 1/56 Willits 73l36 2,975,846 3/61' Bodine -19 FOREIGN PATENTS 492,038 9/38 Great Britain.

RICHARD C. QUEISSER, Primary Examiner.

DAVID SCHONBERG, ROBERT L. EVANS,

' Examiners. 

1. IN A PILE DRIVER HAVING A DRIVING MEANS SUPPORTED IN LEADS, AN APPARATUS FOR DETERMINING THE LOAD BEARING CAPACITY OF A PILE COMPRISING MEANS FOR CONTINUOUSLY RECORDING ON A COMMON TIME UNIT SCALE THE POWER DELIVERED TO THE DRIVING MEANS, MEANS FOR CONTINUOUSLY RECORDING THE RATE OF PENETRATION ON A COMMON TIME UNIT SCALE, AND MEANS FOR CONTINUOUSLY RECORD ON A COMMON TIME UNIT SCALE THE NUMBER OF IMPACTS PER SECOND. 